A geometric criterion for the optimal spreading of active polymers in porous media

Navigation through porous environments poses a major challenge for swimming microorganisms and future microrobots. This study predicts that their spreading becomes optimal when their run length is comparable to the longest available pore length. Efficient navigation through disordered, porous environments poses a major challenge for swimming microorganisms and future synthetic cargo-carriers. We perform Brownian dynamics simulations of active stiff polymers undergoing run-reverse dynamics, and so mimic bacterial swimming, in porous media. In accord with experiments of Escherichia coli, the polymer dynamics are characterized by trapping phases interrupted by directed hopping motion through the pores. Our findings show that the spreading of active agents in porous media can be optimized by tuning their run lengths, which we rationalize using a coarse-grained model. More significantly, we discover a geometric criterion for the optimal spreading, which emerges when their run lengths are comparable to the longest straight path available in the porous medium. Our criterion unifies results for porous media with disparate pore sizes and shapes and for run-and-tumble polymers. It thus provides a fundamental principle for optimal transport of active agents in densely-packed biological and environmental settings.

Automated summary

Efficient navigation through porous environments by swimming microorganisms and microrobots can be optimized by adjusting their run lengths to match the longest straight path available in the porous medium, a criterion termed as the optimal spreading criterion. This criterion unifies results for porous media with different pore sizes and shapes and for run-and-tumble polymers, providing a fundamental principle for achieving optimal transport of active agents in densely-packed biological and environmental settings.